Swainson's hawk (Buteo swainsoni)
Swainson's Hawks are broad-winged Buteos of between 48 and 56 cm in length with females slightly larger than males. Males and females have similar plumage. Swainson's Hawks are polymorphic with pale, light and intermediate morph plumage ranging from dark to light or rufous in color. Most Swainson's Hawks have a sharp contrast between the wing linings and flight feathers. However, some of the darkest Swainson's Hawks do not have this distinction. Swainson's Hawks are distinguishable from other Buteos by their more narrow body and wings, but are still often confused with Broad-winged, White-tailed and Short-tailed Hawks (Bechard et al. 2010).
- Bechard, Marc J., C. Stuart Houston, Jose H. Sarasola and A. Sidney England. 2010. Swainson's Hawk (Buteo swainsoni), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/265
- Goodrich, L.J., and J.P. Smith. 2008. Raptor migration in North America. Pp. 37-149 in K.L. Bildstein, J.P. Smith, E. Ruelas Inzunza, and R.R. Veit (eds.), State of North America's birds of prey Nuttall Ornithological Club, Cambridge, MA, and American Ornithologists' Union, Washington, D.C
- Wheeler, B.K., C.M. White and J.M. Economidy. 2003. Raptors of Western North America: The Wheeler Guide.
- States/US Territories in which the Swainson's hawk, is known to or is believed to occur: Colorado
- US Counties in which the Swainson's hawk, is known to or is believed to occur: View All
- Countries in which the the Swainson's hawk, is known to occur: Canada, Mexico
- Additional species information
|Status||Date Listed||Lead Region||Where Listed|
|Great Lakes-Big Rivers Region (Region 3)|
» Federal Register Documents
No recovery information is available for the Swainson's hawk.
» Critical Habitat
No critical habitat rules have been published for the Swainson's hawk.
» Conservation Plans
» Life History
Swainson's Hawk breeding habitat includes shrub-steppe areas with scattered trees, large shrubs and riparian areas. They will often feed in agricultural areas (Goodrich and Smith 2008, p. 120). Areas they inhabit require at least small tracks of adjacent land containing lightly irrigated agricultural areas particularly with alfalfa and grass hay (their preferred habitat), or non-agricultural areas with low or moderate height vegetated areas (Wheeler 2003, p. 274). Swainson's Hawks nest in trees of a variety of species, but most often small shrubby trees in shrubb-steppe and desert habitats (Goodrich and Smith 2008, p. 120).
Young are fed rodents, rabbits and reptiles. However, when not breeding, adults feed almost exclusively on insects, primarily grasshoppers (Bechard et al. 2010).
Movement / Home Range
The Swainson's Hawk breeding range extends as far north as southern Alberta, Saskatchewan, Manitoba and some areas of British Columbia. In the United States, breeding occurs as far west as California, east into areas of west Minnesota and north Iowa and south into central Texas. Nonbreeding summering individuals can be found in areas of Texas, Oklahoma, Kansas, central Missouri and southern Iowa. The southern extent of the Swainson's Hawk range extends into areas of northern Mexico (Bechard et al. 2010). Swainson's Hawks are long-distance, thermal soaring migrants that travel in large flocks of thousands of individuals and may demonstrate broad front migration across the United States until their convergence point in southern Texas, eastern Mexico and the Mesoamerica corridor. Swainson's Hawks move in large flocks and prefer to utilize thermals for soaring more often than ridgeline updrafts, and are more commonly seen traveling through grassland ecosystems than along leading and diversion lines. Before fall migration in late September, Swainson's Hawks gather (in late August and early September) to feed on grasshoppers in agricultural areas to prepare for the long voyage (Goodrich and Smith 2008, p. 120).
Pair bonding for Swainson's Hawks begins with aerial courtship displays upon return to breeding grounds in spring around March or April. Nest building begins within the 7-15 days of arrival on breeding grounds and lasts about one or two weeks. Nests are typically built in a solitary tree or bush, or a small group or line of trees along a stream. Swainson's Hawks also favor agricultural areas including alfalfa, wheat and other row crops for building nests nearby. A small number of nests have been reported on human structures. Egg laying occurs shortly after lasting from early March until late May depending on the location. Swainson's Hawks do not typically build more than one nest per year but if a clutch or nest is destroyed they may rebuild the nest nearby. Egg incubation is approximately 28-35 days, with female staying on the nest. The female may leave the nest only briefly when the male provides her with food, which she often consumes away from the nest. In these cases the male may incubate the nest briefly. When hatched young are altricial and inactive for the first 8-10 days, but able to stand at about 13-17 days. Young can feed themselves at about 23-26 days, but the female may still feed them for up to 32 days. Juveniles first attempt to fly at 29-33 days and fly at around 38-46 days. For the first 2 weeks or so after fledging juveniles stay around 2km2 from the nest (Bechard et al. 2010).
Pesticides are a large cause of mortality for Swainson's Hawks. Large numbers of Swainson's hawks were killed on their wintering grounds in Argentina in the mid-1990's due to poisoning by a highly toxic organophosphate insecticide that has since been banned. It is unknown whether use of organophosphates in the United States affects Swainson's Hawk populations. Illegal shooting is also a threat to Swainson's Hawk populations (Wheeler 2003, p. 281).
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